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Eastern Tent Caterpillar: Warm, Fuzzy and Icky

By Dave Taft June 13, 2014 6:27 pmJune 13, 2014 6:27 pm

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Credit Dave Taft

The eastern tent caterpillar (Malacosoma americanum) ranks high on the “ick” scale for many New Yorkers. Vilified by gardeners, and frequently mistaken for other more destructive caterpillars like those of the nonnative gypsy moth, it is unfairly cast as a woodlands plague. Children seem to instinctively want to squish them. But beauty can sometimes be found in unlikely places. A close examination of the eastern tent caterpillar reveals a handsome native, well adapted to life in the northeast.

The caterpillars are particularly fond of wild black cherry trees, though they may also be found on apple, hawthorn and other trees in the rose family. Just about any neglected field in New York City has a black cherry tree or two; you’re sure to see them in Floyd Bennett Field, Van Cortlandt Park or the Salt Marsh Nature Center. The caterpillars overwinter within their eggs and chew their way out to feed on their host’s emerging leaves. But the caterpillars are surprisingly intolerant of cold weather, and cannot digest properly when temperatures drop. In order to cope with this inescapable reality of springtime, the caterpillars communally spin the silk tent that gives them their name.

The tent functions as a greenhouse and is carefully situated at the joint of two or more cherry branches. The animals spend nights in the tent and emerge together two or three times a day to feed. The tent also dissuades predators — at least some of them. As unappealing as sticking your head into a webby nest of hairy wriggling caterpillars might be to humans, some birds — cuckoos and orioles in particular — specialize in tweezing out the caterpillars, which they then wipe on tree trunks to remove some of the caterpillars’ hairs before swallowing them or bringing them back to their nests.

After their sixth and final molt at about an inch and half, tent caterpillars descend from the trees searching for quiet crevices in which to spin their cocoons. Their vibrant colors and elaborate patterns could inspire a Persian rug maker. A long, unbroken white stripe trims each of their backs and is surrounded by lavish decorations including sky-blue ovals set among sinuous orange and black stripes and spots. The caterpillars are also fringed from head to tail with beautiful ginger-colored setae (caterpillar hairs), but having spent a lifetime eating fruit tree leaves filled with cyanide compounds, the hairs are just one more distasteful feature in their defense arsenal.

The adult eastern tent caterpillar is a small brown moth. Far less conspicuous than its busy, flashy, caterpillar self, it is also far less destructive. In contrast to the caterpillars’ prodigious appetite, the moths do not feed and live long enough only to mate and lay eggs, which they carefully position to reap next year’s cherry leaves. The cherry, having sacrificed many of its early leaves, grows another crop crowned with flowers that remain unmolested by the now-disinterested eastern tent moths.

Correction: June 22, 2014The N.Y.C. Nature column in some editions last Sunday, about the eastern tent caterpillar, misidentified the poison in the fruit-tree leaves that the eastern tent caterpillar eats. It is made up of cyanide compounds, not arsenic.

A version of this article appears in print on 06/15/2014, on page MB4 of the NewYork edition with the headline: Warm, Fuzzy and Icky.

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